Tlll<: I'TERIDOPHYTA 335 



moss-like appearance which has given the common name to the 

 group. The internal structure of the stem in Lijcopodium is 

 unique, for its fibro-vascular system is a solid, pithless core, made 

 up of alternating Imnds of wood and bast extending across the 

 central cylindcM- (Fig. 208). The anatomy of the other genera is 

 much simpler. 



Sporangia are few and large as compared with those of the 

 ferns, and are borne on the upper or ventral leaf-surface. In 



Fig. 208. — Transverse section (diagrammatic) of the stem of Lrjcopodium. 

 The fibro-vascular cylinder consists of alternating bands of wood and bast. 

 From this cylinder a small leaf-trace departs to each leaf. Wood black, bast 

 dotted. 



the simpler species, a sporangium may arise on an ordinary vege- 

 tative leaf but in most cases these spore-bearing leaves (which 

 here, as elsewhere among the higher plants are known as sporo- 

 phylls) become stout and scale-like, and are grouped in a cone or 

 strohilus at the tip of a branch. The two main orders Lycopodia- 

 les and Selaginellales are distinguished chiefly by their methods 

 of reproduction. 



1. Lycopodiales (Fig. 209). — These are homosporous plants, 

 the spores which they produce being all of one sort, as in the 

 Filicales. The gametophytes vary considerably but tend to 

 develop a stout tuberous, subterranean portion, which may be 

 surmounted ])y a green aerial region on which the sexual organs 

 luv borne (Fig. 210). These are larger and bettor developed than 



